linux-kernel - Re: [PATCH v5 10/11] cpufreq: CPPC: make scaling_min/max_freq read-only when auto

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Message-ID: <66e5ccea-9cc2-429e-856d-e3f420a8b2b2@huawei.com>
Date: Fri, 26 Dec 2025 11:26:41 +0800
From: "zhenglifeng (A)" <zhenglifeng1@...wei.com>
To: Sumit Gupta <sumitg@...dia.com>, <rafael@...nel.org>,
	<viresh.kumar@...aro.org>, <lenb@...nel.org>, <robert.moore@...el.com>,
	<corbet@....net>, <pierre.gondois@....com>, <rdunlap@...radead.org>,
	<ray.huang@....com>, <gautham.shenoy@....com>, <mario.limonciello@....com>,
	<perry.yuan@....com>, <ionela.voinescu@....com>, <zhanjie9@...ilicon.com>,
	<linux-pm@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <acpica-devel@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>
CC: <linux-tegra@...r.kernel.org>, <treding@...dia.com>,
	<jonathanh@...dia.com>, <vsethi@...dia.com>, <ksitaraman@...dia.com>,
	<sanjayc@...dia.com>, <nhartman@...dia.com>, <bbasu@...dia.com>
Subject: Re: [PATCH v5 10/11] cpufreq: CPPC: make scaling_min/max_freq
 read-only when auto_sel enabled

On 2025/12/23 20:13, Sumit Gupta wrote:
> When autonomous selection (auto_sel) is enabled, the hardware controls
> performance within min_perf/max_perf register bounds making the
> scaling_min/max_freq effectively read-only.
> 
> Enforce this by setting policy limits to min/max_perf bounds in
> cppc_verify_policy(). Users must use min_perf/max_perf sysfs interfaces
> to change performance limits in autonomous mode.
> 
> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
> ---
>  drivers/cpufreq/cppc_cpufreq.c | 32 +++++++++++++++++++++++++++++++-
>  1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index b1f570d6de34..b3da263c18b0 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -305,7 +305,37 @@ static unsigned int cppc_cpufreq_fast_switch(struct cpufreq_policy *policy,
>  
>  static int cppc_verify_policy(struct cpufreq_policy_data *policy)
>  {
> -	cpufreq_verify_within_cpu_limits(policy);
> +	unsigned int min_freq = policy->cpuinfo.min_freq;
> +	unsigned int max_freq = policy->cpuinfo.max_freq;
> +	struct cpufreq_policy *cpu_policy;
> +	struct cppc_cpudata *cpu_data;
> +	struct cppc_perf_caps *caps;
> +
> +	cpu_policy = cpufreq_cpu_get(policy->cpu);

Better to use:

	struct cpufreq_policy *cpu_policy __free(put_cpufreq_policy) = cpufreq_cpu_get(policy->cpu);

> +	if (!cpu_policy)
> +		return -ENODEV;
> +
> +	cpu_data = cpu_policy->driver_data;
> +	caps = &cpu_data->perf_caps;

cpu_policy, cpu_data and cpas are only used in the if branch. Just put them
in it.

> +
> +	if (cpu_data->perf_ctrls.auto_sel) {
> +		u32 min_perf, max_perf;
> +
> +		/*
> +		 * Set policy limits to HW min/max_perf bounds. In autonomous
> +		 * mode, scaling_min/max_freq is effectively read-only.
> +		 */
> +		min_perf = cpu_data->perf_ctrls.min_perf ?:
> +			   caps->lowest_nonlinear_perf;
> +		max_perf = cpu_data->perf_ctrls.max_perf ?: caps->nominal_perf;
> +
> +		policy->min = cppc_perf_to_khz(caps, min_perf);
> +		policy->max = cppc_perf_to_khz(caps, max_perf);
> +	} else {
> +		cpufreq_verify_within_limits(policy, min_freq, max_freq);

Why not still using cpufreq_verify_within_cpu_limits()?

> +	}
> +
> +	cpufreq_cpu_put(cpu_policy);
>  	return 0;
>  }
>